sys: sflist: allow usage of all available flag bits

Room for flag bits is function of the struct sfnode alignment.
Define the flag mask accordingly. This gives 2 available bits on 32-bit
architectures and 3 bits on 64-bit architectures.

Signed-off-by: Nicolas Pitre <[email protected]>

Author: Nicolas Pitre

include/zephyr/sys/sflist.h

@@ -12,7 +12,7 @@
   * @brief Flagged single-linked list implementation.
   *
   * Similar to @ref single-linked-list_apis with the added ability to define
-  * two bits of user "flags" for each node. They can be accessed and modified
+  * user "flags" bits for each node. They can be accessed and modified
   * using the sys_sfnode_flags_get() and sys_sfnode_flags_set() APIs.
   *
   * Flagged single-linked list implementation using inline macros/functions.
@@ -213,7 +213,10 @@ static inline void sys_sflist_init(sys_sflist_t *list)
  */
 #define SYS_SFLIST_STATIC_INIT(ptr_to_list) {NULL, NULL}
 
-#define SYS_SFLIST_FLAGS_MASK	((uintptr_t)0x3)
+/* Flag bits are stored in unused LSB of the sys_sfnode_t pointer */
+#define SYS_SFLIST_FLAGS_MASK	((uintptr_t)(__alignof__(sys_sfnode_t) - 1))
+/* At least 2 available flag bits are expected */
+BUILD_ASSERT(SYS_SFLIST_FLAGS_MASK >= 0x3);
 
 static inline sys_sfnode_t *z_sfnode_next_peek(sys_sfnode_t *node)
 {
@@ -272,7 +275,8 @@ static inline sys_sfnode_t *sys_sflist_peek_tail(sys_sflist_t *list)
  * @brief Fetch flags value for a particular sfnode
  *
  * @param node A pointer to the node to fetch flags from
- * @return The value of flags, which will be between 0 and 3
+ * @return The value of flags, which will be between 0 and 3 on 32-bit
+ *         architectures, or between 0 and 7 on 64-bit architectures
  */
 static inline uint8_t sys_sfnode_flags_get(sys_sfnode_t *node)
 {
@@ -283,14 +287,15 @@ static inline uint8_t sys_sfnode_flags_get(sys_sfnode_t *node)
  * @brief Initialize an sflist node
  *
  * Set an initial flags value for this slist node, which can be a value between
- * 0 and 3. These flags will persist even if the node is moved around
- * within a list, removed, or transplanted to a different slist.
+ * 0 and 3 on 32-bit architectures, or between 0 and 7 on 64-bit architectures.
+ * These flags will persist even if the node is moved around within a list,
+ * removed, or transplanted to a different slist.
  *
  * This is ever so slightly faster than sys_sfnode_flags_set() and should
  * only be used on a node that hasn't been added to any list.
  *
  * @param node A pointer to the node to set the flags on
- * @param flags A value between 0 and 3 to set the flags value
+ * @param flags The flags value to set
  */
 static inline void sys_sfnode_init(sys_sfnode_t *node, uint8_t flags)
 {
@@ -302,11 +307,12 @@ static inline void sys_sfnode_init(sys_sfnode_t *node, uint8_t flags)
  * @brief Set flags value for an sflist node
  *
  * Set a flags value for this slist node, which can be a value between
- * 0 and 3. These flags will persist even if the node is moved around
- * within a list, removed, or transplanted to a different slist.
+ * 0 and 3 on 32-bit architectures, or between 0 and 7 on 64-bit architectures.
+ * These flags will persist even if the node is moved around within a list,
+ * removed, or transplanted to a different slist.
  *
  * @param node A pointer to the node to set the flags on
- * @param flags A value between 0 and 3 to set the flags value
+ * @param flags The flags value to set
  */
 static inline void sys_sfnode_flags_set(sys_sfnode_t *node, uint8_t flags)
 {